login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A098450 Largest n-digit semiprime. 6
9, 95, 998, 9998, 99998, 999997, 9999998, 99999997, 999999991, 9999999997, 99999999997, 999999999997, 9999999999989, 99999999999997, 999999999999998, 9999999999999994, 99999999999999989, 999999999999999993, 9999999999999999991, 99999999999999999983 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..100

FORMULA

a(n) = 10^n - A119320(n). - Amiram Eldar, Sep 18 2021

MATHEMATICA

NextSemiPrime[n_, k_: 1] := Block[{c = 0, sgn = Sign[k]}, sp = n + sgn; While[c < Abs[k], While[ PrimeOmega[sp] != 2, If[sgn < 0, sp--, sp++]]; If[sgn < 0, sp--, sp++]; c++]; sp + If[sgn < 0, 1, -1]]; f[n_] := NextSemiPrime[10^n, -1]; Array[f, 18] (* Robert G. Wilson v, Dec 18 2012 *)

PROG

(PARI) apply( A098450(n)={n=10^n; until(bigomega(n-=1)==2, ); n}, [1..20]) \\ M. F. Hasler, Jan 01 2021

(Python)

from sympy import factorint

def semiprime(n): f = factorint(n); return sum(f[p] for p in f) == 2

def a(n):

  an = 10**n - 1

  while not semiprime(an): an -= 1

  return an

print([a(n) for n in range(1, 21)]) # Michael S. Branicky, Apr 10 2021

CROSSREFS

Cf. A098449 (smallest n-digit semiprime), A003618 (largest n-digit prime), A001358 (semiprimes), A119320.

Sequence in context: A000562 A193216 A213019 * A337269 A065456 A052389

Adjacent sequences:  A098447 A098448 A098449 * A098451 A098452 A098453

KEYWORD

base,nonn,changed

AUTHOR

Rick L. Shepherd, Sep 07 2004

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 24 17:29 EDT 2021. Contains 347651 sequences. (Running on oeis4.)